The quality of air in semiconductor processing tools is a major concern in the semiconductor manufacturing industry. Photolithography tools in particular require air of appropriate temperature, humidity and cleanliness (both with respect to particulates and molecular contaminants).
Traditional approaches to air humidity and temperature control use an air conditioning device that, for example, can exchange heat with an air stream and remove or add water vapor to the air stream.
The removal of contaminants from an air stream and, in particular, the removal of molecular contaminants, is traditionally performed with another device. For example, traditional approaches typically involve the use of activated carbon filters and/or combination of adsorptive and chemisorptive medias to control contamination in conjunction with a temperature and/or humidity controlling air-handling device to manage temperature and humidity of delivered air.
Traditional approaches to contaminant removal employ filters, or a series of filters, to remove particulates and molecular contaminants. Particulates are generally viewed as contaminates having a size of greater than about 0.1 microns. Molecular contaminants are generally viewed as those contaminants that form deposits (e.g., organics) and/or inhibit process performance (e.g., bases).
Filters, however, have several problems. Filters increase pressure resistance and thereby increase the pressure drop in the air handling system for a processing tool. Filters also have a limited service life, requiring that the filters be eventually removed and replaced. Such replacement can require downtime of the associated semiconductor processing tools to replace the filter elements and add to the overall cost of ownership of the process tool.
In addition, many filters have a limited capability in mitigating optics-damaging volatile organic compounds, especially in the lower molecular weight ranges because lower molecular weight organics are typically difficult to adsorb. Increasing the capability and/or capacity of a filter generally means adding greater amounts of adsorptive media, which in turn further increases pressure resistance and cost.
The filtration media of a filter may itself introduce particulate contamination requiring downstream particulate filtration. In addition, the filtration media of a filter may itself introduce chemical contamination. For example, traditional filtration methods involving the use of highly acidic medias may introduce damaging acid anions into the air stream, such as sulfur containing oxides, such as, for example, SO2.
In addition, the filter media of a filter, especially of some traditional chemical filters, can create problems with air stream temperature and humidity control For example, highly acidic sulfonated medias (traditionally used for the removal of basic compounds, such as ammonia and amines) are by their chemical nature prone to reversible exothermic reactions with water (for example, hydration reaction). This heat and humidity interaction causes difficulty in the feedback control of air stream temperature and humidity. Difficulties in air stream humidity and temperature control are especially problematic in photolithography, as the typical objective is to manage temperature and/or humidity variation to ultra-low levels (for example, variations of less than tens of a milliKelvin in temperature, and variations of less than few tenths of a percent in relative humidity). Difficulties in air stream humidity and temperature control may substantially increase the time necessary to achieve control stability, for example, during a start-up process of a photolithography tool. An increase in the time to achieve control stability is directly related to tool availability, a production metric of concern to the semiconductor industry.